Various types of cutting tools use rotatable bits which can be clamped in selected positions on a cutting tool holder or body. In one such cutting tool--see German Pat. No. 1,552,296--a clamping bolt can be inserted in a bore in the cutting body and threaded therein to clamp the cutter bit with the conical head against the body itself. The clamping bolts fits into a circular conical enlargement of the bore which is offset with respect to the center of the clamping hole in the cutter bit. When the clamping bolt is screwed into the tapped bore of the holder, the conical portion of the bolt will engage at the inner wall of the conical recess therein and is laterally elastically deflected. This elastic deflection presses the cutter bit against abutment surfaces on the body. The enlarged portion of the bore must be big enough to permit lateral deflection of the bolt; thus, its diameter in all respective section planes is greater than the diameter of the conical portion of the clamping bolt in the same section plane. Consequently, the conical portion of the clamping bolt engages the inner wall of the conical recess only along a single line. The maximum diameter of the clamping head of the clamping bolt must be smaller than the smallest diameter of the hole in the cutter bit since, otherwise, the cutter bit cannot be placed on the clamping bolt without entire removal thereof from the tool. The clamping head of the bolt also engages the cutter bit along the single line.
When engaging the bolt with a cutter bit which, in turn, engages the respective abutment surfaces on the tool, and the bolt is resiliently deflected, the bolt is no longer guided with respect to the tool body. The position of the engagement line between the conical portion of the bolt and the inner wall of the conical recess in the tool body, as well as between the clamping head of the bolt and the bit itself is indeterminate due to play in the threads between the bolt and the body. In many machine tools, and particularly in machine tools in which the tool elements are highly stressed, it is important to ensure that the contact zone between the clamping head and the inner wall of the cutter bit has a defined predetermined position with respect to the abutment surfaces on the tool body.